U.S. Pat. No. 4,904,807 ('807) discloses a process of manufacturing ethylene oxide comprising reacting ethylene and free oxygen in a reactor in the presence of methane to form ethylene oxide (in an effluent containing carbon dioxide and argon); withdrawing the effluent from the reactor; removing ethylene oxide from the reactor effluent to obtain a recycle stream; removing carbon dioxide and argon from the recycle stream to obtain a treated recycle stream; supplying the treated recycle stream to the reactor; and supplying additional reactants and methane to the reactor.
Additional reactants, ethylene and free oxygen-containing gas, are supplied to the reactor to replace the reactants which reacted to ethylene oxide. Methane is supplied to maintain the methane concentration at such a level that its presence is beneficial to the efficiency of the reaction as described in U.S. Pat. No. 3,119,837.
Carbon dioxide is a by-product of the reaction and part of the carbon dioxide is removed to maintain the concentration of carbon dioxide below a predetermined level.
Argon enters into the process with the free oxygen-containing gas. In order to maintain the argon concentration below a predetermined level, a portion is removed from the recycle stream downstream of the removal of ethylene oxide. In addition trace amounts of nitrogen enter into the process with the free oxygen-containing gas.
In the process of the '807 patent, removing argon comprises separating a side stream from the recycle stream, passing the side stream to the feed inlet of a membrane unit, removing an argon-containing stream from the permeate outlet of the membrane unit, removing a retentate stream from the retentate outlet of the membrane unit, and adding the retentate stream to the recycle stream.
As the flow through the membrane is large, the area of the membrane is large as well. The area of the membrane could be reduced and the overall ethylene oxide process could be made more efficient by increasing the rate of the extraction of argon through the membrane used to extract it. Furthermore, given the combination of combustible reactants, intermediates, and products in ordinary reaction conditions, additional process measures which make the process safer yet would be beneficial.